This invention deals with primer compositions. More specifically, this invention describes primer compositions which bind room temperature-curable silicone rubbers, or room temperature-curable silicone-modified organic rubbers, firmly to the surface of various base materials.
Large quantities of room temperature-curable silicone rubbers have been used as sealants in various structures and buildings because the rubber itself exhibits a durability far superior to the durability of other organic rubbers. At the same time, room temperature-curable silicone-modified organic rubbers have appeared and are occasionally used as sealants in structures and buildings. Structures and buildings employ various base materials such as metals such as aluminum, steel and stainless steel; painted construction materials such as acrylic resin-coated aluminum; hard inorganic construction materials such as glass, tile and building stone and porous inorganic base materials such as mortar, concrete and ALC which is a foamed concrete. It is very important that a room temperature-curable silicone rubber or room temperature-curable silicone-modified organic rubber be tightly bound to the above base materials. For this reason, these base materials are usually treated with various primers and then coated with a room temperature-curable silicone rubber or room temperature-curable silicone-modified organic rubber which is simultaneously adhered and cured. However, some of these base materials, such as pure aluminum, surface-treated aluminum, stainless steel, various rein-coated aluminums and mortar are difficult to adhere and seal with the result that a silicone rubber of silicone-modified organic rubber will peel at the interface between the rubber and base material prior to extensive degradation and loss of elasticity in the rubber. Thus, there is a requirement for a primer which has a high adhesive strength for a long term and in particular has a high adhesive strength for a long term when immersed in water.
Primers which consist of mixtures of epoxy resins and organofunctional silanes are known in the prior art, but since unmodified epoxy resins are employed, miscibility with the silicone component in the form of silanes is inadequate. As a result, it is impossible to obtain a homogeneous, durable adhesive film. Thus, these products are unsatisfactory as primers.
To overcome the above drawbacks, the present inventors have previously proposed one-component primer compositions based on organotitanium esters and silicone-modified epoxy resins which contain epoxy groups and silicon-bonded alkoxy groups. As a result of additional research, it has been discovered that when certain alkoxysilanes or their partial hydrolyzates are mixed with these compositions, the durability of adhesion is improved and the storage stability of these one-component primers is improved.